The prior art already includes a process for controlling the operation of an optical channel carried by a welding tool and conducting a welding laser beam, at operational power, from a laser source to a welding location.
It is known to utilize a welding tool such as a laser beam welding iron for welding operations in confined spaces, especially in the tubes of a nuclear reactor steam generator cooled by pressurized water. These steam generators comprise a bundle consisting of a large number of tubes of small diameter (approximately 20 mm), bent into a U shape and fixed at each of their ends by crimping in a tubular plate of large thickness. That part of the steam generator which is situated below the tubular plate delimits a water reservoir into which the ends of the tubes of the bundle open. The stresses to which the tubes are subjected give rise, in some cases, to fissures in the walls of these tubes. It is known to carry out the repair of these tubes by sleeve coupling of the tubes. For this purpose, repair sleeves are fixed in the tubes by welding, by means of a laser beam welding iron which is inserted into the water reservoir and into the tubes.
Applicant's FR-A-89/08,635 shows a welding set, comprising a laser beam welding iron which is utilized to carry out the sleeve coupling of tubes of a steam generator and which is disposed within the water reservoir of the generator.
The welding iron comprises an optical channel which essentially comprises an optical fiber conducting the laser beam along the iron from a laser source, disposed outside the water reservoir, to a welding head of the (iron, and optical means, disposed in this head, which are adapted to focus the laser beam on a welding location.
In order to carry out the welding operations under good conditions, the optical operation of the welding iron is controlled and the good transmission of the power of the laser beam in the optical channel of the iron is ensured. To this end, the power emitted at the exit of the laser source is generally measured before entry of the beam into the optical fiber. The measurement of the power at the exit of the optical fiber or at the exit of the welding head requires a space adequate to arrange means for sampling the beam and means for measuring the power of the beam. In the case of a welding operation within the tubes of a steam generator, there is not adequate space to insert such means. Moreover the extraction of the welding iron out of the water reservoir, for example with a view to carrying out a measurement of the power of the beam, is detrimental to the work sequence and the equipment.